Drills having replaceable cutting tips mounted on shanks are known. The cutting heads and shanks display continuous and complementing configuration as fluted drills. To this end, each shank has structure for retaining and rotating an associated cutting head. The associated cutting head has complementing structure for being retained and rotated by the shank. While these devices will operate under some circumstances, closer analysis reveals that their useful lives are potentially unduly limited. More specifically, the retaining and drive structure of the shank is subject to deformation and failure during its service life due to concentration of stresses imposed during when drilling on uneven or angled surfaces.
A conventional cutting head and a rotary tool can be derived, for example, from WO 2008/072840 A2 or from the applicant's applications PCT/EP 2015/056288 or DE 10 2015 211744.8, which were unpublished as of the filing date.
The rotary tool is a so-called “modular” rotary tool, which extends in the axial direction along an axis of rotation and has two coupling parts, namely a support and a cutting head. The cutting head is interchangeably mounted on the support. To that end, the support typically has on its front side two fastening bars that face each other and are separated by flutes that limit accommodation of pins. Inserted into this pin receptacle is a coupling pin of the cutting head. This is accomplished by rotating the cutting head around the axis of rotation in relation to the support. This rotation typically forms a clamping connection between the cutting head and the support, clamping together the two coupling parts. At the same time, no other fastening elements, for example screws or the like, are arranged. The fastening by clamping is accomplished between the outer peripheral surfaces of the coupling pin and the inner peripheral surfaces of the pin receptacle.
Also arranged are two corresponding surfaces for transmitting torque from the support to the cutting head. These torque driving surfaces are referred to below in brief as torque surfaces.
Another similar modular rotary tool can be derived from DE 10 2012 200 690 A1.
Modular rotary tools can be divided into two different types. In a first type, like the one derived from, for example, WO 2008/072840 A2, the torque surfaces extend outward radially up to an outermost periphery of the cutting head, also called “drill ridges.” According to a second variant, like the one described, for example, in the two unpublished applications cited above or also in DE 10 2012 200 690 A1, the torque surfaces are formed directly on the coupling pin as its outer peripheral surfaces, which interact with corresponding inner peripheral surfaces of the fastening bars.
Both the torque surfaces and the clamping surfaces of the cutting head and of the support are installed in pairs opposite each other in a coupled state when the cutting head is thus inserted into the support. At the same time, the corresponding clamping surfaces form in each instance a press fit; i.e., in the area of the clamping surfaces, the coupling pin has an allowance vis-à-vis the pin receptacle.
In some of the applications cited above, formed for an axial pullout safety on each coupling pin are roughly horizontal stop surfaces that interact with corresponding stop surfaces of the support, in order to thus guarantee a positive fit in the axial direction for the cutting head. This positive fit prevents the cutting head from being pulled out from the support in an axial direction, for example when the rotary tool is withdrawn from the drill hole after a drilling procedure.
In WO 2008/072840 A2, a circumferential groove in the form of a recess is formed to form this axial pullout safety on the coupling pin. In a similar manner, in PCT/EP 2015/056288 or DE 10 2015 211744.8, the stop surface is formed by radial grinding in the form of recesses.
In DE 10 2012 200 690 A1, on the other hand, the coupling pin is formed to form a rear grip for an axial, dovetail-type pullout safety.